This Invention relates to a system, process and apparatus for the removal of pollutants from carrier gas streams resulting from chemical, industrial, heat and power, smelting, refining, combustion and other processes, and particularly to cleaning such carrier streams of acid gases and other water-soluble or insoluble pollutant gases, vapors and/or particulates.
Air pollution has long been recognized as a serious problem in the health and ecological areas and otherwise. Recognizing this fact, in 1970 The Clean Air Act was passed by the US Congress, and subsequently further legislation and regulations have been enacted by federal, state and local jurisdictions in order to control and/or reduce air pollution.
The pollution in the air may comprise solid or liquid particulate matter and various innocuous or noxious gases found in many streams as well as gaseous effluent or by-product pollution in numerous process streams. The legislation and regulations have attempted to eliminate or limit the amount of pollutants discharged into the atmosphere by polluted gas streams.
The pollutants found in the air may vary widely in form, size and chemical nature. For example, the particulate matter may be liquids or solids that, in turn, may be chemically active or inert. The particles may vary in size from substantially smaller than 0.01 micron up to a fraction of an inch and may include metal or mineral values of economic significance. The gaseous pollutants may be relatively innocuous gases, such as carbon dioxide, or highly toxic gases including gases such as hydrogen sulfide, sulfur dioxide, carbon monoxide, or various of the nitrogen oxides. Some of the gaseous pollutants may be further reacted in the atmosphere to form acids or other substances that may have deleterious effects on the environment.
One method of reducing pollution and attempting to meet the emission standards of the various legislation and regulations has been to attempt to control the pollutants at the source. However, this approach is not always available and, in many instances, is neither possible nor practicable. Moreover, many of the pollutants are submicronic particles. Such submicronic particulate, though constituting only a very small portion of the total weight of the emission, may represent the vast majority of the number of particles emitted and also may represent the vast majority of the total toxic material emitted. Thus, the contribution of the submicronic particulate to the degradation of the ambient atmosphere is disproportionate to its relatively small weight. As recognition of this effect grows, it is expected that legislatures and other control agencies will place greater emphasis on the removal of fine particulate, particularly in view of the availability of new instrumentation to detect such smaller and smaller sized particulates.
Various methods and types of apparatus have been employed over the years to remove particulates from gas streams where these pollutants cannot be removed at their source. One category of such equipment is fabric filters. In the filter separator a screen having interstitial openings of any desired size is placed as a barrier to the flow of the particulate-containing gas stream. A common form of the filter separator is known as a bag-house which comprises a large number of fabric bags of felt or woven fabrics having a fine mesh to trap the particulate from the gas stream. While the bag-house separator is one of the most effective of the prior art devices for the removal of fine particulate, it has several inherent disadvantages that prevent its adoption for many processes. First, the bag-house is a relatively large installation and may employ several thousand fabric bags. As a result of its complexity, the bag-house is expensive to install and maintenance and operating costs are high due to the necessity for frequent cleaning and replacement of the bags. Secondly, the operating temperature is limited by the nature of the fabric material so that cooling of the gases to be treated is frequently necessary. Finally, while the bag-house is quite effective for particulate removal down to a size of about 1 micron, it is not well adapted to the removal of pollutants such as sulfur dioxide where some type of chemical reaction is necessary nor to the removal of particles below 1.0 micron in size which may be found in fumes and smog.
Another commonly used device is the mechanical separator, the so-called cyclone or centrifugal separator. In this apparatus the particulate-containing gas is generally introduced tangentially into a cylindrical or conical vessel and, as the direction of the gas stream is changed, the particulate is separated therefrom. While the cyclone is effective for large particulate that will readily separate from a gas stream due to gravitational or inertial forces, its efficiency decreases with smaller particulate and becomes largely ineffective with respect to particulate which is less than about 10 microns in size. Also, the energy requirements of the cyclone are proportional to the pressure drop through the cyclone and increase rapidly as the particulate decreases in size.
A still further category of gas cleaning equipment includes the precipitator that employs electrostatic forces. In this device, a particulate-containing gas stream is charged to one polarity and is then passed between oppositely charged plates that, in turn, attract the particulate. The particulate may then be removed by mechanical means. The electrostatic precipitator becomes largely ineffective for particulate less than about 2 to 3 microns in size. In addition to relatively high capital costs, the precipitator is expensive to operate and its performance tends to deteriorate in time. Where the effluent gas contains combustible material there may also be safety hazards that inhibit the use of the precipitator. Other inadequacies of the precipitator include the inability to remove sulfur dioxide and sensitivity to particulate resistivity.
Some separation may result from the action of gravitational forces though, in the above equipment, these forces were not intentionally exploited. Thus, if desired, a particulate-containing gas stream may be introduced into a large settling or stilling chamber where the velocity is reduced essentially to zero. Again, this device is most effective for large particulate. As the particulate becomes smaller, the time required for settling increases.
The aforementioned dry types of devices and systems have not been particularly effective or very economical. Thus there have been proposed various wet systems. During the 1970""s a number of improvements were made in the wet scrubbing technology. Ejector driven or fan driven scrubbers employing centrifugal separators or separated flow separators were developed which included the first use of the mixing capability of the free jet nozzle. Such apparatus is shown, for example, in U.S. Pat. Nos. 3,852,408; 3,852,409 and 4,141,701. Due to the development of much smaller droplets, which were more effectively mixed with the gas stream, both particulate and acid gases were collected simultaneously with very high efficiency. Though far more efficient than the venturi scrubbers, these devices still required about 20-40 inches of water pressure drop to collect the desired amount of pollutants. In common with other wet scrubbing systems, the collection efficiency increased as the amount of energy delivered to the system increased.
The art has also developed pollution control systems that represent a combination of earlier developed devices. See, for example, U.S. Pat. No. 3,894,851. Thus it has been common to use a spray chamber followed by a cyclone separator or a venturi scrubber; a venturi jet scrubber followed by a separator; or two venturi jet scrubbers followed by a separator. U.S. Pat. No. 3,852,408 discloses a system for removing particulate and gaseous sulfur dioxide (or other acid gases) comprising a spray chamber for conditioning the polluted gas stream and removing large particulate, a hot-water drive and a chemical injection unit for driving the gas and capturing the remaining particulate and sulfur dioxide in water droplets, means for enlarging the droplets, and a cyclone separator for separating the water droplets containing the particulate and sulfur dioxide reaction products from the stream of cleaned gas. A similar system is shown in U.S. Pat. No. 3,852,409 wherein the driving system utilizes a steam ejector and a water spray in place of the hot water drive. A still further development is shown in U.S. Pat. No. 4,141,701 which discloses a drive system employing supersonic steam, air, or gas ejectors or subsonic free jet nozzles as the drive unit and an aerodynamic flow separating system to separate the pollutant-containing water drops from the cleaned gas. Another development is disclosed in U.S. Pat. No. 4,272,499. In this patent there is disclosed a process in which carrier gas is driven through a conduit, in part by a fan or blower, and the carrier gas is passed through a turbulent free jet emitted from a supersonic nozzle and containing a large number of small high velocity liquid droplets, the mixture of the carrier gas and free jet is passed through a subsonic nozzle, injecting additional liquid as droplets into the mixture, retaining the mixture in a mixing tube to promote further growth of the liquid droplets and separating the liquid droplets from the carrier gas. A still further development is taught in U.S. Pat. No. 4,921,886 wherein the process includes introducing a stream containing vapor and liquid droplets into a stream containing carrier gas and alkaline sorbent material, and thereafter a portion of the vapor is condensed and the alkaline sorbent material reacted with the acid gases to form reaction products, after which the products of reaction and the remaining alkaline sorbent material are separated from the carrier gas.
However, all these wet processes have a number of drawbacks and disadvantages. For one, their ability to separate smaller and smaller submicronic particulates is problematic and there is a need for a method, apparatus and system for being able to remove smaller particles than can be removed by the afore-mentioned processes. Additionally, the price of providing suitable power to run those processes has increased, particularly due to the increased cost of fuel to provide that power, whereby there is a need for a process that not only removes small particulates but is able to do so by requiring less power to operate the process so that the process is more economically feasible to operate.
This invention provides a method, system and apparatus for more efficiently removing pollutants, and particularly particulates, from a polluted carrier gas stream and additionally being able to remove small submicronic particulates, as well as other various gases and vapors. Additionally, in the invention the initial size of the pollutant is not controlling as is the case in prior art processes.
The new and novel method, system and apparatus of this invention utilizes moisture-containing sonic or supersonic waves moving through a subsonic flow of a polluted gas stream to modify or grow the pollutants in the gas stream so that they become removable or separable from the polluted gas stream.
In one aspect the process of this invention involves removing small sized pollutants from a polluted gas stream containing the pollutants, the improvement comprising: passing moisture-containing sonic or supersonic shock waves through a subsonic flow of the polluted gas stream as the polluted gas stream exits a subsonic free jet nozzle and enters into a contiguous chamber having an area of pressure of  less than 14.7 psia adjacent the region of the free jet nozzle exit, whereby the pollutants are modified or grown as they pass through the shock waves and thereby become removable or separable from the polluted gas stream.
In a further aspect of this invention the process for removing pollutants from a polluted gas stream containing the pollutants comprises:
(a) providing a subsonic flow of the polluted gas stream through a subsonic free jet nozzle into a chamber having an area of pressure of  less than 14.7 psia;
(b) introducing into the chamber, in the area of pressure of  less than 14.7 psia and at one or more points adjacent entry of the polluted gas stream from the free jet nozzle into the chamber, moisture-containing sonic or supersonic shock waves which pass through the polluted gas stream in the chamber causing the pollutants to be modified or grown in size; and
(c) removing the modified or grown pollutants from the stream of polluted gas.
In a further aspect of this invention there is provided apparatus or a system for removal of pollutants from a polluted gas stream, wherein the apparatus or system comprises:
(d) a subsonic free jet nozzle with an exit for providing a flow of said polluted gas stream;
(e) a chamber having an entry end and exit end, the entry end being connected to the subsonic free jet nozzle and surrounding the exit of the subsonic free jet nozzle for receiving the flow of the polluted gas stream in an area of the chamber having a pressure of  less than 14.7 psia as the stream of polluted gas exits the subsonic free jet nozzle;
(f) one or more sonic or supersonic nozzles surrounding the exit of the subsonic free jet nozzle for providing moisture-containing sonic or supersonic shock waves for moving through the flow of polluted gas in the chamber and modifying or growing in size the pollutants in the polluted gas stream for removal of the pollutants from the polluted gas stream; and
one or more separators connected to the chamber for separating the modified or grown pollutants from the polluted gas stream.
In the process or method according to this invention the pollutants in the polluted gas stream may comprises acidic or other gases or vapors, or small particulate matter that may be of micronic or submicronic size. In the process of this invention the acidic or other gases or vapors may be modified by reaction with suitable reagents to render them removable or separable from the polluted gas stream. The passage of the moisture-containing sonic or supersonic shockwaves through the polluted gas stream causes the reagent(s) to readily react with the gases or vapors to produce a product readily removable or separable from the polluted gas stream. The particulate pollutants in the polluted gas stream are caused to grow in size as they pass through the moisture-containing sonic or supersonic shock waves so that they become more readily removable or separable from the polluted gas stream. Submicronic particulates are caused to grow to at least micronic or greater sized particulates as they pass through the sonic or supersonic shock waves.
The reagent(s) for reaction with the acidic or other gases or vapors may be introduced into the system by being introduced into the stream of polluted gas upstream of the subsonic free jet nozzle, i.e., before the gas stream flows through the subsonic free jet nozzle, or may be introduced into the system in the moisture-containing sonic or supersonic shock waves which contact the subsonic flow of polluted gas as it exits the subsonic free jet nozzle exit.
The sonic or supersonic shock waves are preferably introduced into the polluted gas stream in the chamber in the area of pressure of  less than 14.7 psia as a canopy of essentially continuous shock waves from a plurality of sonic or supersonic nozzles surrounding the exit of the free jet nozzle from which the polluted gas stream enters the chamber. In a particularly preferred embodiment of this invention the sonic or supersonic shock waves are shock waves of air and water or are such shock waves of steam.
In the apparatus or system of this invention the separator(s) may be any suitable separator useable for separating the pollutants from the polluted gas stream after the pollutants are modified or grown, but are preferably cyclone separators, or filter separators such as a bag house. Such separators are preferably connected to the exit end of the chamber. The separator(s) may also be drains provided in the chamber for removal of liquefied pollutants, or gravity separated particulates or the like.
The sonic or supersonic nozzles for introducing the shock waves into the polluted gas stream in the area of the chamber having a pressure of  less than 14.7 psia will generally comprise a plurality of such nozzles surrounding the exit end of the subsonic free jet nozzle, and preferably will comprise at least three such sonic or supersonic nozzles located approximately 120xc2x0 apart around the exit of the subsonic free jet nozzle. However, it will be appreciated that any suitable number of nozzles arranged and spaced any suitable degrees apart may be employed in accordance with this invention.
In a further aspect of this invention, the method or process and apparatus or system may utilize a sequential series of two or more connected series of subsonic free jet nozzles and adjoining chambers with sonic or supersonic nozzles for modifying or growing the pollutants in a polluted gas stream to be treated in accordance with this invention. In such a series of apparatus components, the entry end of the second chamber is connected to the exit end of the first chamber and surrounds a second subsonic free jet nozzle attached to the exit end of the first chamber, and additionally comprises one or more sonic or supersonic nozzles surrounding the second free jet nozzle for providing additional moisture-containing sonic or supersonic shock waves for moving through the flow of polluted gas stream in the second chamber for modifying or growing in size the pollutants in the polluted gas stream in the second chamber. In such an arrangement, either or both chambers may be provided with drain separators, and one or more separators of the cyclone type of fabric filter type are connected to the exit end of the second or last chamber in the series.
We describe this new apparatus and system using sonic or supersonic shock waves for removing pollutants from a polluted gas stream as a Thermo-Chemical Gas Cleaner (TCGC) since it is vastly different in operation than previously used gas cleaning apparatus and systems. The TCGC system provides a higher level of cleaning performance than previous systems and also has a lower energy requirement for the reasons explained hereinafter. In the TCGC the polluted gas is moved by a subsonic fan and subsonic free jet nozzles, and the gas is cleaned by the sonic or supersonic nozzles in a chamber of  less than 14.7 psia and accelerates the polluted gas flowing from the subsonic nozzle. Additionally, the TCGC converts the thermal energy of the steam and/or water and the compression energy of the sonic or supersonic nozzles into kinetic working energy in the cleaning process. In the process of the invention, in addition to the growth and cleaning function of the sonic or supersonic nozzles, the exit flow produces increased flow velocity and reduced pressure in the process.